<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>固定定位</title>
        <style>
            .fu{
                background-color: lemonchiffon;
            }
            .fu>div{
                width: 100px;
                height: 100px;
            }
            .z1{
                background-color: springgreen;
                position: relative;
                z-index: 5;
            }
            .z2{
                background-color: violet;
                /*固定定位：会脱离文档流（释放布局空间）
                移动参照物：html根元素*/
                position: fixed;
                right: 0;
                bottom: 0;
            }
            .z3{
                background-color: aqua;
            }
        </style>
    </head>
    <body>
        <div class="fu">
            <div class="z1"></div>
            <div class="z2"></div>
            <div class="z3"></div>
        </div>
    </body>
</html>